Questions and Answers of Computer Communications

Prior to persistent connections, one separate TCP connection was used to fetch each URL. Analyze the advantages of persistent connections over the old HTTP paradigm of one connection per data
Before the deployment of DNS, a simple text file (HOSTS.TXT) centrally maintained at the SRI Network Information Center was used to enable mapping between host names and addresses. Each host
A user on the host 170.210.17.145 is using a Web browser to visit www.example.com.In order to resolve the “www.example.com” domain to an IP address, a query is sent to an authoritative name
Secondary name servers periodically query the primary to check whether the zone data has been updated. Regardless of how many resource records the zone data contains, the secondary name servers need
With the widespread use of x-DSL and cable-modem technologies, many home users now host Web sites on their own desktop computers. As their IP addresses are dynamically assigned by their Internet
Type dig www.example.com A in order to get the IP address of www.example.com.What’s the TTL of the A record returned in the response? Wait a while, and repeat the query. Why has the TTL changed?
Choose a root server, and use the dig tool to send it a query for the IP address of www.example.com, with the RD (Recursion Desired) bit set. Does it support recursive lookups? Why or why not?
Discuss the advantages of using several stub resolvers along with a caching-only name server, instead of several full resolvers.
The dig tool provides easy interactive access to the DNS. The dig tool is available for UNIX and Windows operating systems. It can also be used from the Web. Here are two sites that, at the time of
We query an authoritative name server for the example.com zone in order to get the IP address of www.example.com, the Web site of a large company. We get eight A records in response to our query. We
Name servers can be accessed on UDP port 53 as well as on TCP port 53. When is each protocol used, and why?
What’s the main difference between a primary and a secondary name server?
A DNS resolver typically issues a query using UDP but may also use TCP. Is there a problem using TCP for this purpose? If so, what do you suggest is the solution? Hint:Consider the TCP and UDP
Classify a DNS resolver and a DNS name server as client, server, or both.
Although TCP is a full-duplex protocol, SMTP uses TCP in a half-duplex fashion.The client sends a command and then stops and waits for the reply. How can this halfduplex operation fool the TCP
Users are free to define and use additional header fields other than the ones defined in RFC 822. Such header fields must begin with the string “X-”. Why?
We’ve seen that the character sequence “.” indicates the end of mail data to an SMTP-server. What happens if the mail data itself contains that character sequence?
Suppose you need to send one message to three different users: http://user1@example.com, user2@example.com, and user3@example.com. Is there any difference between sending one separate message per
Explain the differences between the intended use for the quoted-printable and base64 encodings.
Excluding the connection establishment and termination, what is the minimum number of network round trips to send a small e-mail message using SMTP?
Electronic mail systems differ in the manner in which multiple recipients are handled.In some systems, the originating user agent or mail sender makes all the necessary copies and these are sent out
What is the function of the cache in HTTP?
Explain the difference between the recursive technique and the iterative technique in DNS.
What is the difference between a domain and a zone?
What is a DNS resource record?
What is the difference between a name server and a resolver in DNS?
What is DNS?
Briefly explain radix-64 encoding.
What is the difference between a MIME content type and a MIME transfer encoding?
What is the difference between RFC 821 and RFC 822?
Consider that we have two applications using MPLS with traffic engineering. One application is delay sensitive (DS), such as a real-time voice or video application. The other application is
In an MPLS-enabled IP network, isn’t it the case that the IP layer at each router still has to examine the IP header to make a routing decision? Explain.
Figure 23.5 indicates that the topmost label in a label stack is adjacent to the encapsulating layer 2 header and the label at the bottom of the stack is adjacent to the header of the transported
In the TCP/IP protocol suite, it is standard practice for the header corresponding to a given protocol layer to contain information that identifies the protocol used in the next higher layer. This
The MPLS specification allows an LSR to use a technique known as penultimate hop popping. With this technique, the next-to-last LSR in an LSP is allowed to remove the label from a packet and send it
What is meant by a constraint-based routing algorithm?
Explain label stacking.
What is an MPLS label switched path?
What is an MPLS forwarding equivalence class?
What is traffic engineering?
RFC 2679 defines the inverse percentile of x for a set of measurements to be the percentage of all values … x. What is the inverse percentile of 103 ms for the measurements in Problem 22.14?
RFC 2330 defines the median of a set of measurements to be equal to the 50th percentile if the number of measurements is odd. For an even number of measurements, sort the measurements in ascending
For the one-way and two-way delay metrics, if a packet fails to arrive within a reasonable period of time, the delay is taken to be undefined (informally, infinite).The threshold of reasonable is a
RFC 2330 (Framework for IP Performance Metrics) defines percentile in the following way. Given a collection of measurements, define the function F(x), which for any x gives the percentage of the
A single video source transmits 30 frames per second, each containing 2 Mbits of data. The data experiences a delay jitter of 1s. What size of delay buffer is required at the destination to eliminate
Now consider an alternative set of equations for EF PHB:where Dj = departure time of the jth EF packet to arrive at this node and destined to depart from I; measured at the time the last bit leaves
One way to quantify the EF PHB performance requirement is with the following set of equations relating to packets leaving a node through some interface I to an external communications link:where dj =
In RSVP, because the UDP/TCP port numbers are used for packet classification, each router must be able to examine these fields. This requirement raises problems in the following areas:a. IPv6 header
Provide three examples (each) of elastic and inelastic Internet traffic. Justify each example’s inclusion in their respective category.
It is clear that if a router gives preferential treatment to one flow or one class of flows, then that flow or class of flows will receive improved service. It is not as clear that the overall
When multiple equal-cost routes to a destination exist, OSPF may distribute traffic equally among the routes. This is called load balancing. What effect does such load balancing have on a transport
What is meant by per-hop behavior?
What is the difference between FIFO queueing and WFQ queueing?
List and briefly describe the three categories of service offered by ISA.
What are the major functions that are part of an ISA?
What is the difference between elastic and inelastic traffic?
What is the Integrated Services Architecture?
In a typical Mobile IP implementation in a foreign agent, the agent maintains a visitor table that contains information about the mobile nodes currently visiting this network.What entries are
In a typical Mobile IP implementation in a home agent, the agent maintains a mobility binding table to map a mobile node’s home address to its care-of address for packet forwarding. What entries
Again referring to Figure 21.12, assume that A is a mobile node and that LAN X is a foreign network for A. Assume that an IP datagram arrives at R1 from the Internet to be delivered to A. Show the
This problem refers to Figure 21.12. Suppose that LAN Z is the home network for host E and that D sends a block of data to E via IP.a. Show the PDU structure, including the fields of the IP header
Some researchers argue that the optimal placement of the center of the shared tree(i.e., the rendezvous point in PIM) is crucial for achieving good delay characteristics for the multicast traffic.
“In sparse-mode PIM, for the route between a given source and a given destination, the RP-based tree may be replaced with a path that is the shortest unicast path from source to destination.”
Most multicast routing protocols, such as MOSPF, minimize the path cost to each group member, but they do not necessarily optimize the use of the Internet as a whole. This problem demonstrates this
With multicasting, packets are delivered to multiple destinations. Thus, in case of errors (such as routing failures), one IP packet might trigger multiple ICMP error packets, leading to a packet
Multicast applications commonly use UDP or RTP (Real-Time Transport Protocol)as their transport protocol. Multicast applications do not use TCP as its transport protocol. What’s the problem with
Multicast applications call an API function on their sockets in order to ask the IP layer to enable or disable reception of packets sent from some specific IP address(es)to a specific multicast
IGMP membership queries include a “Max Resp Code” field that specifies the maximum time allowed before sending a responding report. The actual time allowed, called the Max Resp Time, is
In IGMPv1 and IGMPv2, a host will cancel sending a pending membership report if it hears another host claiming membership in that group, in order to control the generation of IGMP traffic. However,
IGMP specifies that query messages are sent in IP datagrams that have the Time to Live field set to 1. Why?
In a manner similar to Figure 21.3, show the spanning tree from router B to the multicast group.
and comment on the results.
In the discussion of Figure 21.1, three alternatives for transmitting a packet to a multicast address were discussed: broadcast, multiple unicast, and true multicast. Yet another alternative is
A connected graph may have more than one spanning tree. Find all spanning trees of this graph:
Most operating systems include a tool named “traceroute” (or “tracert”) that can be used to determine the path packets follow to reach a specified host from the system the tool is being run
Under what circumstances would a mobile node choose to use each of the types of address referred to in the preceding question?
What are the two different types of destination addresses that can be assigned to a mobile node while it is attached to a foreign network?
What is the relationship between Mobile IP discovery and ICMP?
List and briefly define the capabilities provided by Mobile IP.
What is Openflow?
What is an SDN domain?
What network requirements led to the development of SDN?
What operations are performed by IGMP?
List and briefly explain the functions that are required for multicasting.
Summarize the differences among unicast, multicast, and broadcast addresses.
List some practical applications of multicasting.
A TCP entity opens a connection and uses slow start. Approximately how many round-trip times are required before TCP can send N segments?
In Equation (20.5), rewrite the definition of SRTT(K + 1) so that it is a function of SERR(K+1). Interpret the result.
Derive Equation (20.2) from Equation (20.1).
One difficulty with the original TCP SRTT estimator is the choice of an initial value.In the absence of any special knowledge of network conditions, the typical approach is to pick an arbitrary
Jacobson’s congestion control algorithm assumes most packet losses are caused by routers dropping packets due to network congestion. However, packets may be also dropped if they are corrupted in
Analyze the advantages and disadvantages of performing congestion control at the transport layer, rather than at the network layer.
A source generates data in terms of bursts: 3 MB bursts lasting 2 msec once every 100 msec. The network offers a bandwidth of 60 MB/sec.a. The source passes through a leaky bucket with a capacity of
Consider a token bucket with a capacity of 1 Mb, a token replenishment rate of 2 Mbps, and an outgoing network link of capacity 10 Mbps. Suppose that an application produces 0.5-Mb burst every 250 ms
The token bucket scheme places a limit on the length of time at which traffic can depart at the maximum data rate. Let the token bucket be defined by a bucket size B octets and a token arrival rate
For a frame relay network to be able to detect and then signal congestion, it is necessary for each frame handler to monitor its queueing behavior. If queue lengths begin to grow to a dangerous
Consider the packet-switching network depicted in Figure 20.14. C is the capacity of a link in frames per second. Node A presents a constant load of 0.8 frames per second destined for A’. Node B
A congestion control scheme used with ATM (Available Bit Rate) is to decrease the allowable data rate in response to congestion with the following equation.Ratenew = Rateold - Rateold * RDF where RDF
When the sustained traffic through a packet-switching node exceeds the node’s capacity, the node must discard packets. Buffers only defer the congestion problem;they do not solve it. Consider the
A proposed congestion control technique is known as isarithmic control. In this method, the total number of frames in transit is fixed by inserting a fixed number of permits into the network. These

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